Method and system for utilizing undersampling for crystal leakage cancellation

ABSTRACT

Methods and systems for utilizing undersampling for crystal leakage cancellation are disclosed and may include undersampling a composite signal comprising a desired signal and leakage signals due to one or more clock signals. Measured DC signals generated by each of the undersampled signals may be reduced by adjusting the phase and/or amplitude of the clock signals. The undersampling may be performed at one or more of the one or more clock signals, or at integer sub-harmonics of the clock signals. The composite signal may include a signal received by a wireless system or a signal to be transmitted by the wireless system. The undersampled signals may be low-pass filtered. The desired signal may include in-phase and quadrature signals or a polar signal. The undersampling may be performed by one or more sample and hold circuits and the clock signals may be generated utilizing one or more crystal oscillators.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

[Not Applicable]

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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MICROFICHE/COPYRIGHT REFERENCE

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FIELD OF THE INVENTION

Certain embodiments of the invention relate to wireless communication.More specifically, certain embodiments of the invention relate to amethod and system for utilizing undersampling for crystal leakagecancellation.

BACKGROUND OF THE INVENTION

In 2001, the Federal Communications Commission (FCC) designated a largecontiguous block of 7 GHz bandwidth for communications in the 57 GHz to64 GHz spectrum. This frequency band may be used by the spectrum userson an unlicensed basis, that is, the spectrum is accessible to anyone,subject to certain basic, technical restrictions such as maximumtransmission power and certain coexistence mechanisms. Thecommunications taking place in this band are often referred to as ‘60GHz communications’. With respect to the accessibility of this part ofthe spectrum, 60 GHz communications is similar to other forms ofunlicensed spectrum use, for example Wireless LANs or Bluetooth in the2.4 GHz ISM bands. However, communications at 60 GHz may besignificantly different in aspects other than accessibility. Forexample, 60 GHz signals may provide markedly different communicationschannel and propagation characteristics, not least due to the fact that60 GHz radiation is partly absorbed by oxygen in the air, leading tohigher attenuation with distance. On the other hand, since a very largebandwidth of 7 GHz is available, very high data rates may be achieved.Among the applications for 60 GHz communications are wireless personalarea networks, wireless high-definition television signal, for examplefrom a set top box to a display, or Point-to-Point links.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with the present invention as set forth inthe remainder of the present application with reference to the drawings.

BRIEF SUMMARY OF THE INVENTION

A system and/or method for utilizing undersampling for crystal leakagecancellation, substantially as shown in and/or described in connectionwith at least one of the figures, as set forth more completely in theclaims.

Various advantages, aspects and novel features of the present invention,as well as details of an illustrated embodiment thereof, will be morefully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram illustrating an exemplary wireless communicationsystem, in connection with an embodiment of the invention.

FIG. 2 is a block diagram illustrating an exemplary crystal leakagecancellation system, in accordance with an embodiment of the invention.

FIG. 3 is a block diagram illustrating an exemplary RF signal spectrum,in accordance with an embodiment of the invention.

FIG. 4 is a block diagram illustrating an exemplary undersampled RFsignal spectrum, in accordance with an embodiment of the invention.

FIG. 5 is a flow diagram illustrating an exemplary transmitter leakagesignal cancellation process, in accordance with an embodiment of theinvention.

FIG. 6 is a flow diagram illustrating an exemplary receiver leakagesignal cancellation process, in accordance with an embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Certain aspects of the invention may be found in a method and system forutilizing undersampling for crystal leakage cancellation. Exemplaryaspects of the invention may comprise undersampling a composite signalcomprising a desired signal and one or more leakage signals due to oneor more clock signals. One or more measured DC signals generated by eachof the undersampled signals may be reduced by adjusting a phase and/oran amplitude of the one or more clock signals. The undersampling may beperformed at one or more of the clock signals, or at integersub-harmonics of the clock signals. The composite signal may comprise asignal received by a wireless system or a signal to be transmitted bythe wireless system. The undersampled signals may be low-pass filtered.The desired signal may comprise in-phase and quadrature signals or apolar signal. The undersampling may be performed by one or more sampleand hold circuits and the clock signals may be generated utilizing oneor more crystal oscillators.

FIG. 1 is a diagram illustrating an exemplary wireless communicationsystem, in accordance with an embodiment of the invention. Referring toFIG. 1, there is shown an access point 112 b, a computer 110 a, aheadset 114 a, a router 130, the Internet 132 and a web server 134. Thecomputer or host device 110 a may comprise a wireless radio 111 a, ashort-range radio 111 b, a host processor 111 c, a host memory 111 d anda processor 111 e. There is also shown a wireless connection between thewireless radio 111 a and the access point 112 b, and a short-rangewireless connection between the short-range radio 111 b and the headset114 a.

Frequently, computing and communication devices may comprise hardwareand software to communicate using multiple wireless communicationstandards. The wireless radio 111 a may be compliant with a mobilecommunications standard, for example. There may be instances when thewireless radio 111 a and the short-range radio 111 b may be activeconcurrently. For example, it may be desirable for a user of thecomputer or host device 110 a to access the Internet 132 in order toconsume streaming content from the Web server 134. Accordingly, the usermay establish a wireless connection between the computer 110 a and theaccess point 112 b. Once this connection is established, the streamingcontent from the Web server 134 may be received via the router 130, theaccess point 112 b, and the wireless connection, and consumed by thecomputer or host device 110 a. The processor 111 e may control signalprocessing, clock signals and delays, for example, in the short rangeradio 111 b.

It may be further desirable for the user of the computer 110 a to listento an audio portion of the streaming content on the headset 114 a.Accordingly, the user of the computer 110 a may establish a short-rangewireless connection with the headset 114 a. Once the short-rangewireless connection is established, and with suitable configurations onthe computer enabled, the audio portion of the streaming content may beconsumed by the headset 114 a. In instances where such advancedcommunication systems are integrated or located within the host device110 a, the radio frequency (RF) generation may support fast-switching toenable support of multiple communication standards and/or advancedwideband systems like, for example, Ultrawideband (UWB) radio. Otherapplications of short-range communications may be wirelessHigh-Definition TV (W-HDTV), from a set top box to a video display, forexample. W-HDTV may require high data rates that may be achieved withlarge bandwidth communication technologies, for example UWB and/or60-GHz communications.

Undersampling may be utilized to remove leakage from clock signals in 60GHz wireless systems. Leakage signals may be reduced and/or eliminatedby configuring the clock signal for an undersampling process to be aninteger sub-harmonic frequency of the clock signal that may be leakinginto the desired output signal.

FIG. 2 is a block diagram illustrating an exemplary crystal leakagecancellation system, in accordance with an embodiment of the invention.Referring to FIG. 2, there is shown a digital signal processor (DSP)201, a mixer 203, amplifiers 205 and 207, a sample and hold (S/H)circuit 209, and a low pass filter (LPF) 215. There is also shown acrystal signal 217, a data signal 219, a DC output signal 221 and an RFsignal 223. The S/H circuit 209 may comprise a capacitor 211 andswitches 213A and 213B.

The DSP 201 may comprise suitable circuitry, logic and/or code that mayenable processing of baseband signals that may be up-converted andtransmitted by an antenna, for example, not shown in FIG. 2, or receivedby an antenna and down-converted. For transmission, the DSP 201 mayreceive as inputs a 13 MHz crystal signal 217 and the data signal 219.For reception, the DSP 201 may generate the data signal 219 as anoutput. The crystal signal 217 may comprise a clock signal for the DSP201 and/or other devices in the wireless system. Clock signals may“leak” from baseband circuitry into subsequent stages of a wirelesssystem, as described further with respect to FIG. 3. The DSP 201 may beenabled to generate in-phase and quadrature (I and Q) signals or polarsignals for up-conversion, amplification and transmission.Alternatively, the DSP 201 may be enabled to process I and Q and/orpolar signals from down-converted received signals. Leakage signals maybe present in received signals via spurious clock signals received by anantenna, for example.

The mixer 203 may comprise suitable circuitry, logic and/or code thatmay enable up-converting a received baseband signal utilizing an inputlocal oscillator (LO) signal, indicated by f_(LO) in FIG. 2. Theresulting output signal may be an RF signal suitable for amplificationand transmission. In another embodiment of the invention, the mixer 203may be enabled to down-convert a received signal.

The amplifier 205 may comprise suitable circuitry, logic and/or codethat may enable amplifying the signal generated by the mixer 203 fortransmission. In another embodiment of the invention, the amplifier maybe enabled to amplify a signal received by an antenna, for example. Thegain of the amplifier 205 may be variable, and the amplified signal maycomprise the RF output signal 223. The RF signal 223 may be suitable forfurther amplification before transmission via an antenna, for example.In another embodiment of the invention, the RF signal 223 may comprise areceived RF signal.

The amplifier 207 may comprise suitable circuitry, logic and/or codethat may enable further amplification of the RF signal 223 prior tosubsampling by the S/H circuit 209. The S/H circuit 209 may comprisesuitable circuitry, logic and/or code that may enable sampling thesignal received from the amplifier 207. The switches 213A and 213B maybe enabled to open and close at a sampling frequency, which may be thesame as or an integer sub-harmonic of the crystal signal 217. Thecapacitor 211 may enable the holding of a sampled signal beforecommunicating it to the LPF 215.

The LPF 215 may comprise suitable circuitry, logic and/or code that mayenable filtering signals at frequencies higher than a cutoff frequency.The LPF 215 cutoff frequency may be configured to filter signals exceptthose at or near DC.

In operation, the DSP 201 may generate baseband signals to beup-converted and amplified such that they may be transmitted to thewireless medium. A clock signal, such as the crystal signal 217, mayleak from the DSP 201 through the mixer 203 and the amplifier 205 intothe RF signal 223. By undersampling the RF signal 223 at an integersub-harmonic of the crystal signal 217 in the S/H circuit 209, theharmonics of the crystal signal 217 may be “folded” down to DC, suchthat the DC voltage measured at the output of the LPF 215 may indicatethe amount of leakage of the crystal signal 217 into the RF signal 223.By adjusting the phase and amplitude of the crystal signal 217 at theinput of the DSP 201, a minimum in the DC voltage may be obtained at theoutput of the LPF 221. In this manner, the leakage of the crystal signal217 into the RF signal 223 may be minimized and/or eliminated.

The sampling frequency for the S/H 209 may be generated utilizing thecrystal signal 217 and dividing the frequency by an integer. In thismanner, the harmonics of the crystal frequency that may be leaking intoother sections of the wireless system may be at DC due to undersampling.

The invention is not limited in the frequency of the crystal signal 217,13 MHz, for example, or in the number of clock signals. Accordingly, anydesired frequency and the leakage from any number of clock signals maybe reduced and/or eliminated by utilizing a plurality of S/H circuitsand low pass filters. Each S/H circuit may sample at a frequency thatmay be equal to or an integer sub-harmonic of the particular clocksignal. Additionally, the invention may comprise a receiver, in that theRF signal 223 may comprise a received signal, the amplifier 205 maycomprise an amplifier for a received signal, such as an LNA for example,and the mixer 203 may be enabled to down-convert a received signal tobaseband. Whether the signal to be undersampled is a signal to betransmitted or one that has been received, the undersampling process maybe identical.

FIG. 3 is a block diagram illustrating an exemplary RF signal spectrum,in accordance with an embodiment of the invention. Referring to FIG. 3there is shown an RF spectrum 300 comprising a desired signal 301 and acrystal leakage signal 303. The RF spectrum 300 may be substantiallysimilar to the RF signal 223, described with respect to FIG. 2. Thecrystal leakage signal 303 may be different than a blocker signal, whichmay comprise an interfering signal received by the wireless system. Thecrystal leakage signal 303 may comprise a signal leaking through thesystem that may be generated by a clock signal utilized by the circuitryin the wireless system. Thus, the leakage signal 303 may comprise theclock signal itself, a 13 MHz clock signal, for example, or a harmonicof the clock signal. To avoid interference from a leakage signal, the RFspectrum 300 may be undersampled at integer sub-harmonics of any clocksignal that may cause leakage. This may be performed on a signal to betransmitted or on a received signal, which may comprise leakage signalsfrom clock signals in the wireless system.

Undersampling a signal at an integer sub-harmonic frequency may resultin a DC signal corresponding to the leakage signal. Signals that are notharmonics of the undersampling frequency may have non-zero frequencysignals in the baseband after subsampling, so that they may be filteredout with a low pass filter, such as the LPF 215 described with respectto FIG. 2. In this manner, the DC voltage may be measured and maycorrespond to the magnitude of the leakage signal. This is describedfurther with respect to FIG. 4.

FIG. 4 is a block diagram illustrating an exemplary undersampled RFsignal spectrum, in accordance with an embodiment of the invention.Referring to FIG. 4, there is shown an undersampled frequency spectrum400 comprising an undersampled crystal leakage signal 401 and anundersampled data signal 403. The undersampled data signal 403 may beremoved utilizing a low pass filter, such as the LPF 215 described withrespect to FIG. 2, resulting in a DC output signal, the undersampledcrystal leakage signal 401. By adjusting the phase and amplitude of theclock signal that may be the source of the leakage signal, the DC outputvoltage may be minimized and/or eliminated, indicating a minimizedand/or eliminated leakage signal.

FIG. 5 is a flow diagram illustrating an exemplary transmitter leakagesignal cancellation process, in accordance with an embodiment of theinvention. Referring to FIG. 5, in step 503, after start step 501, adata signal and a clock signal may be processed by a signal processor.In step 505, the processed signal may be up-converted to RF generatingan output signal that may be transmitted. In step 507, the up-convertedsignal may be undersampled at an integer sub-harmonic of the clocksignal frequency. The undersampled signal may be low pass filtered instep 509, to result in a DC output signal. The phase and amplitude ofthe clock may then be adjusted in step 511 to minimize and/or eliminatethe DC signal, which may minimize and/or eliminate the leakage signal,followed by end step 513.

FIG. 6 is a flow diagram illustrating an exemplary receiver leakagesignal cancellation process, in accordance with an embodiment of theinvention. Referring to FIG. 6, in step 603, after start step 601, an RFsignal may be received. In step 605, the received signal may beundersampled at an integer sub-harmonic of the leakage signal. In step607, the received RF signal may be amplified and down-converted tobaseband. The undersampled signal may be low pass filtered in step 609,to result in a DC output signal. The phase and amplitude of the clocksignal may then be adjusted in step 611 to minimize and/or eliminate theDC signal, which may minimize and/or eliminate the leakage signal,followed by end step 613.

In an embodiment of the invention, a method and system are disclosed forundersampling a composite signal comprising a desired signal 219 and oneor more leakage signals due to one or more clock signals 217. One ormore measured DC signals 221 generated by each of the undersampledsignals may be reduced by adjusting a phase and/or an amplitude of theone or more clock signals 217. The undersampling may be performed at oneor more of the clock signals 217, or at integer sub-harmonics of theclock signals 217. The composite signal may comprise a signal receivedby a wireless system or a signal to be transmitted by the wirelesssystem. The undersampled signals may be low-pass filtered. The desiredsignal 219 may comprise in-phase and quadrature signals or a polarsignal. The undersampling may be performed by one or more sample andhold circuits 209 and the clock signals 217 may be generated utilizingone or more crystal oscillators.

Certain embodiments of the invention may comprise a machine-readablestorage having stored thereon, a computer program having at least onecode section for utilizing undersampling for crystal leakagecancellation, the at least one code section being executable by amachine for causing the machine to perform one or more of the stepsdescribed herein.

Accordingly, aspects of the invention may be realized in hardware,software, firmware or a combination thereof. The invention may berealized in a centralized fashion in at least one computer system or ina distributed fashion where different elements are spread across severalinterconnected computer systems. Any kind of computer system or otherapparatus adapted for carrying out the methods described herein issuited. A typical combination of hardware, software and firmware may bea general-purpose computer system with a computer program that, whenbeing loaded and executed, controls the computer system such that itcarries out the methods described herein.

One embodiment of the present invention may be implemented as a boardlevel product, as a single chip, application specific integrated circuit(ASIC), or with varying levels integrated on a single chip with otherportions of the system as separate components. The degree of integrationof the system will primarily be determined by speed and costconsiderations. Because of the sophisticated nature of modernprocessors, it is possible to utilize a commercially availableprocessor, which may be implemented external to an ASIC implementationof the present system. Alternatively, if the processor is available asan ASIC core or logic block, then the commercially available processormay be implemented as part of an ASIC device with various functionsimplemented as firmware.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext may mean, for example, any expression, in any language, code ornotation, of a set of instructions intended to cause a system having aninformation processing capability to perform a particular functioneither directly or after either or both of the following: a) conversionto another language, code or notation; b) reproduction in a differentmaterial form. However, other meanings of computer program within theunderstanding of those skilled in the art are also contemplated by thepresent invention.

While the invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiments disclosed, but that the present inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A method for wireless communication in a wireless system, said methodcomprising: undersampling a composite signal comprising a desired signaland one or more leakage signals, said one or more leakage signals due toone or more clock signals; and adjusting one or both of a phase and anamplitude of said one or more clock signals, to reduce one or moremeasured DC signals generated by each of said undersampled signals. 2.The method according to claim 1, comprising undersampling said compositesignal at one or more frequencies that are equal to one or more of saidone or more clock signals.
 3. The method according to claim 1,comprising undersampling said composite signal at one or morefrequencies that are integer sub-harmonics of said one or more clocksignals.
 4. The method according to claim 1, wherein said compositesignal is a signal received by said wireless system.
 5. The methodaccording to claim 1, wherein said composite signal is a signal to betransmitted by said wireless system.
 6. The method according to claim 1,comprising low-pass filtering each of said undersampled signals.
 7. Themethod according to claim 1, wherein said desired signal comprisesin-phase and quadrature signals.
 8. The method according to claim 1,comprising undersampling said composite signal utilizing one or moresample and hold circuits.
 9. The method according to claim 1, comprisinggenerating one or more of said one or more clock signals utilizing oneor more crystal oscillators.
 10. A system for wireless communication,the system comprising: one or more circuits in a wireless system thatenable undersampling a composite signal comprising a desired signal andone or more leakage signals, said one or more leakage signals due to oneor more clock signals; and said one or more circuits enables adjustmentof one or both of a phase and an amplitude of said one or more clocksignals, to reduce one or more measured DC signals generated by each ofsaid undersampled signals.
 11. The system according to claim 10, whereinsaid one or more circuits enable undersampling of said composite signalat one or more frequencies that are equal to one or more of said one ormore clock signals.
 12. The system according to claim 10, wherein saidone or more circuits enable undersampling of said composite signal atone or more frequencies that are integer sub-harmonics of said one ormore clock signals.
 13. The system according to claim 10, wherein saidcomposite signal is a signal received by said wireless system.
 14. Thesystem according to claim 10, wherein said composite signal is a signalto be transmitted by said wireless system.
 15. The system according toclaim 10, wherein said one or more circuits enable low-pass filtering ofeach of said undersampled signals.
 16. The system according to claim 10,wherein said desired signal comprises in-phase and quadrature signals.17. The system according to claim 10, wherein said one or more circuitsenable undersampling of said composite signal utilizing one or moresample and hold circuits.
 18. The system according to claim 10, whereinsaid one or more circuits enable generation of one or more of said oneor more clock signals utilizing one or more crystal oscillators.
 19. Adevice for wireless communication, said device comprising: a circuitthat operates to undersample a composite signal comprising a desiredsignal and a leakage signal, said leakage signal being related to aclock signal; and a processor that operates to adjust one or both of aphase and an amplitude of said clock signal according to saidundersampled composite signal.
 20. The device according to claim 19,wherein the undersampled signal is an analog signal.